Session: Tuesday Morning, December 3

Time: 9:40

The contribution of interaural time differences (ITDs) to the localization
of virtual sound sources with and without head motion was examined. Listeners
estimated the apparent azimuth, elevation, and distance of virtual sources
presented over headphones. Stimuli (3-s, white noise) were synthesized from
minimum-phase representations of nonindividualized head-related transfer
functions (HRTFs); binaural magnitude spectra were derived from the minimum
phase estimates and ITDs were represented as a pure delay. During dynamic
conditions, listeners were encouraged to move their heads; head position was
tracked and stimuli were synthesized in real time using a Convolvotron to
simulate a stationary external sound source. Two synthesis conditions were
tested: (1) both interaural level differences (ILDs) and ITDs correctly
correlated with source location and head motion and (2) ITDs correct, no ILDs
(flat magnitude spectrum). Head movements reduced azimuth confusions primarily
when interaural cues were correctly correlated, although a smaller effect was
also seen for ITDs alone. Externalization was generally poor for ITD-only
conditions and was enhanced by head motion only for normal HRTFs. Overall, the
data suggest that, while ITDs alone can provide a significant cue for azimuth,
the errors most commonly associated with virtual sources are reduced by
location-dependent magnitude cues.